Dr. Gilles Charbit, Standards and ResearchMediaTek Inc.
24th June, 2021CW Non-Terrestrial Networks SIG
An introduction to Release-17 Non-
Terrestrial Networks in 3GPP Radio Access
Network
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Motivation for Non Terrestrial Networks
Mobile cellular network today covers >60% population, but <40% landmass
- Human distribution ≠ Machine distribution
- Need for connected machines in areas where population density is low or un-existent.
- Need for coverage and high resilience of 5G services.
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Status of 3GPP NTN Activities
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Rel-17 New Radio NTN Work Item
Rel-17 IoT NTN Study Item (completed in June) followed by Work Item
SA: System ArchitectureCT: Core and TerminalsRAN: Radio Access NetworkSI: Study ItemWI: Work Item
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Satellite System - Transparent payload architectureExample
The GateWay station consist of a directional high-power antenna system and a Remote Radio Unit (RRU) connected to a Base Band Unit (BBU) via a Common Public Radio Interface (CPRI).
The service access link between satellite and user equipment (UE) operate around 1.5 GHz or 2 GHz in the L band or S band respectively.
The feeder link between satellite and GateWayoperate at higher frequencies in C band around 5 GHz or Ka band around 20 GHz.
Beam foot print diameter can be very large – e.g. 100 km - 3500 km for GEO and 50 km - 1000 km for LEO (3GPP TR 38.821 NR NTN)
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Satellite system with transparent payload
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Key Ideas
Common radio interface for terrestrial and satellite links
- Shared radio for better economies of scales
Modify NR / IoT radios for GEO and LEO satellite links
- Link Budget Feasibility – e.g. GEO UL in S or L bands for NR NTN with UE Power Class 3 (23 dBm) and channel bandwidth 360 kHz with CNR in the order of -10 dB
- Long Propagation Delay requires timing relationship adaptations and UE pre-compensation – e.g. GEO with x100s ms and LEO with x10s ms Round Trip Delays
- Huge Doppler Shift requires UE pre-compensation – e.g. LEO with x10s kHz Doppler shift
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LEO: Low Earth OrbitMEO: Medium Earth OrbitGEO: Geostationary Earth Orbit
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UL Synchronization NR / IoT Devices predict and compensate the serving satellite delay and Doppler shift
before transmitting on return link.
- Using broadcast Ephemeris format Position and Velocity
- Using Ephemeris format Keplerian orbital parameters
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NTN gNB System
3GPP RAN3 defined NTN gNB to include Satellite, Feeder link, NTN GateWay, and non-
NTN infrastructure gNB functions
This means UE pre-compensation requirement / testing stops at satellite in 3GPP RAN4
3GPP RAN4 specified UL frequency error requirement is ±0.1 ppm (over NR-Uu) and
additional from “NTN-Payload + Feederlink + NTN-GW” is negligible
3GPP RAN4 specification of UL timing error requirement is under discussion
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Tracking Area and Paging
Tracking Area Update (TAU) and pagingsolution is needed due to LEO satellite movement
Avoid unnecessary TAUs on cell reselection by Idle devices
Fixed Tracking Area on the ground for moving cells or earth fixed cells
Multiple Tracking Area Codes (TACs) are broadcast per cell
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Summary
3GPP will specify NR NTN and IoT NTN systems in Release-17 timeframe
Shared radio in device to support terrestrial and satellite links in GEO and LEO constellations
Further enhancements of NTN are expected in Release 18 for NR NTN and IoT NTN
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